I haven't written anything serious in a while, but I would like to get back into writing non-fiction. In particular, I want to write about "big ideas" that interest me; however, I realize that writing that has nothing to do with people may not be as interesting as writing that involves people. (Of course this isn't an absolute, but I'd argue that in general, non-fiction that is a little more "personal" and people-focused is at least a little more compelling.)
I remember that some of my favorite non-fiction books were about ideas rather than people's lives, but they usually found a way to focus on people and their interaction with those ideas.
My question is: How does one go about involving people in a book that's secretly more or less about one or more ideas? For example, if I wanted to write a book about grammar, what are some ways to get readers interested in the book on a more personal level?